Module 9 - Electron Transport Chain Flashcards
Electron transport chain is..
series of protein complexes embedded in mitochondrial membrane
○E- captured from donor molecules are transferred through these complexes
What are complexes found in the e transport chain
NADH dehydrogenase, succinate dehydrogenase, cytochrome c reductase, cytochrome c oxidase, ATP synthase
What are the mobible carrier involved in etc
ubiquinone and cytochrome c
What are other key components of ETC
NADH and its e-, H+ , O2, water and ADP and Pi which combine to make ATP
Give a breif overview of the electron transport chain
FUCK THIS QUESTION
●At start of e- transport chain two e- passed from NADH into NADH dehydrogenase complex
○One H for each e- coupled with this
●Next 2 e- transferred to ubiquinone
○Ubiquinone is called mobile transfer molecule which moves e- to cytochrome b-c1 complex to cytochrome c
●Cytochrome c then accepts each e- one at a time and one H+ pumped through complex as each e- is transferred
● Next in the cytochrome oxidase complex, 4 e- required that interact with molecular oxygen to form two water molecules
○Other 4 H+ are pumped across membrane
○This series of H+ pumping creates gradient
○The potential energy in this gradient is used by ATP synthase to make ATP from ADP and inorganic phosphate
What is the structure of the electron transport chain (protein compelces)
Made of 5 protein compleces embedded w/in inner mitochondrial membrane
Protein complex 1,2,3,4,5
What is role of the first complex
- in general the role of the first complex is
1. Accept 2 e- from NADH and shuttle them along
2. Pump 4 protons out of mitochondrial matrix and into intermembrane space
What is the role of coenzyme Q and cytochrome c
● Coenzyme Q shuttles e- through complex 1 and 2 (causes transport of 4 H+) to complex III and cytochrome c shuttles e- from complex III to complex IV
Why do we need coenzyme Q and cytochrome c
electrons dont dissfuse well through hydrophobic interior of membrane
- COenzyme Q and cytochrome c are lipid soluble and can transport the electrond
Do protein complexes accept electrons? Why or why not
- protein compelx doesnt, redox centres w/in protein complex accept electrons
What is the function of redox centers, where are they located
-Since protein complexes themselves arent reversible reduced/oxidized, redox centers can be reversible reduced and oxidizes (like Nad+ and NADH)
How many redox centers are in a protein complex
Proteins complexes contain a combination of two or more redox centers
What are the types redox centers in a protein complexes
○Fe-S clusters
○Copper (Cu)
○Cytochromes
○Coenzymes
What happens to the electrons on NADH and FADH (what complexes..)
NADH donates e- to complex I, complex I passes it to complex III then complex IV
FADH2 It donates its e- to complex II (which is logical and convenient since it’s already there anyways). Then complex II passes it along to complex III then complex IV
What is FADH2 in cirtric acid cycle
Electron donor but also coenzyme that is prosthetic group that’s covalently bound to enzyme succinate dehydrogenase which is part of complex II
What is shutte of electrons driven by
- reduction of potentials of coenzymes and each individual redoc center until final e- acceptor (O2)
What is the final reduction
oxygen catalyzed by enzyme cytochrome oxidase making 2 H2O which is part of complex IV
What is reduction potential
Affinity something as for e-
What is the relative reduction potential of NADH and Oxygen during the beginning of ETC
NADH has lowest reduction potential (least affinity for e-) whereas oxygen has highest reduction potential (highest affinity)
What happens to the redox centers between NADH and oxygen
you pass from protein complex I to III to IV they have increasing reduction potential
Describe what happens in Complex 1: NADH to Ubiquinone
- NADH transfers 2 e- and 1H+ to complex 1
- Complex 1 uses 2e- to pump 4 H+ from matrix into inter membrane space
- Then the two e- are transfer to Coenzyme Q (QH2)
Describe what happens in Complex 2: Succinate to Ubiquinone
- FAD accept two e- from succinate and becomes FADH2
- the electrons from FADH2 pass through iron-sulfur centers to ubiquinone (Coenzyme Q) (QH2)
- IT DOES NOT PUMP PROTEONS
- capture and donates protons
Describe what happens in Complex 3: Ubiquinone to Cytochrome C oxidoreductase
- Coenzyme Q’s reduce 2 molecules of cytochrome c
- electrons pass through Iron sulfur clusters, cytochrome b and cytochrome c
- Clearance of e- from reduced Quinones via Q cycle results in 4 H+ to be pumped into inter membrane space
Describe Complex 4: Cytochrome C to O2
- Four electrons (From cytochrome c) reduce 1 Molecule of oxygen to 2 molecules of water
- Four protons are picked up from matrix for this process
- ANother 2 H are passed from matrix into inter membrane space
What happens each time electrons pass through protein complexes. What is it used for
- each time e- pass through protein complex w/ lower reduction potential to redox centre w/ high reduction potential; energy is released
- The complex uses the energy released to drive proton pumping mechanism that pumps proteins out of matrix and into inter membrane space
How many Protons does each complex pump out per pair of electrons
●Complex I and III each pump 4 protons for each pair of electrons that pass through and Complex iV pumps out only two protons and Complex II pumps nothing
What is the chemiosmotic gradient
The removal of protons from the matrix and deposition of protons in the intermembrane space creates a concentration difference of protons across the inner membrane (chemoosmotic gradient)
What is the only way for protons to move to inner mitochondrial membrane
Through specific transport protein
What is the gradient in nature
Electrochemical
Why is it called electrochemical in nature
○chemical in nature in terms of creating a lower pH of the outside of the inner membrane
○‘electrical’ in natural because of the positive charge of the protons needed to reach equilibrium by entering mitochondrial matrix where charge is negative
What does the chemiosmotic gradient able to do
- it has potential energy stored
- energy is used to drive synthesis of ATP by process called oxidative phosphorylation of ADP to ATP in the complex V
In What complex does the oxidative phosphoyrlation of ADP occur
ATP, is catalyzed by complex V which is also known as F1-F0 ATP synthase that is composed of multiple subunits
Describe the strucutre of Complex V
- aka F1-F0 ATP synthase composed of multiple subunits
- F0 subunit: Protein channel that spans inner mitochondrial membrane, responsible for allowing protons to enter matrix. Integral membrane protein. Its energy is transferred to F1 to catalyze phosphorylation
- rotates when a new hydrogen ion enters, once three protons/h enter the matrix space, there is enough energy in the ATP synthase complex to synthesize one ATP
- F1 subunit: bulbous portion on matrix side of inner membrane. Has the ATP synthase enzyme. Its soluble in maxtrix and individually catalyzes the hydrolysis of ATP.
- F1+F0 are connected by protein stalk
- looks like mushroom protruding into the matrix on the inside of the inner membrane.
How does complex V work?
● One hydrogen ion enters the ATP synthase complex from the intermembrane space a second hydrogen ion leaves it on the matrix space
● Upper part of the ATP synthase complex rotates when a new hydrogen ion enters, once three protons/h enter the matrix space, there is enough energy in the ATP synthase complex to synthesize one ATP
○ Energy in the hydrogen ion gradient is used to make ATP
● Proton enters ATP synthase and exits into the matrix space
● Once three more h atoms have crossed the membrane, ATP is made
● Keeps going until there is an equal number of protons on each side of the inner membrane, no more energy left
● In biological systems, a gradient is always maintained
○ Mitochondrial hydrogen ion gradient is generated as electrons pass through three membrane complexes
How is the gradient maintained
Mitochondrial hydrogen ion gradient is generated as electrons pass through three membrane complexes
What drives the ATP synthase in F1 subunit
When protons pass through F0 channel and stalk from outside to inside of matrix
○proton serves to drive the molecular motor of the ATP synthase which has an ADP and an inorganic phosphate (Pi) present in the active cell
○Proton actually drives the conformation change in the active site and drives the catalysis of the formation of a new high energy phosphoanhydride bond in ATP
How many protons are pumped out as a result of NADH
● Each NADH that donates its electrons to the electron transport chain at complex I, a total of 10 protons are pumped out
How many protons are pumped out as a result of FAHD2
● Each FAH2 that donates its electrons through complex II, a total of only 6 protons are pumped out
How many ATP can NADH yeild and why
3 ATP (per mole of O2 consumed) due to 10 protons pumped out (Need 3/ATP)
How many ATP can FADH2 yield
2 ATP (per mole of O2 consumed) due to 6 protons
How many ATP are generated per glucose molecule that is oxidized (and from which processes)
38 ATP
From Glucose to Pyruvate and Pyruvate to Acetyl CoA and then citric acid cycle
How does NADH from glycolysis reach the mitochondria Matric
- It never is able to cross into the inner membrane
there is no transport for NADH
What are mechanism by which NADH can donate its electrons to transverse into the membrane. Explain them
- Two pathways that provide electrons for NADH generated in the cytosol to ETC:
- Glycerol-3-phosphate
- Malate aspartate shuttle
